During standard diesel engine combustion, oxides of nitrogen (NO, NO.sub.2, etc.) are produced which result in pollution emissions from car and truck exhaust. Well known in the art is the fact that an effective way to reduce nitrous oxides (NO.sub.x) in the exhaust of a diesel engine, without also increasing particulate emissions, is to reduce the peak temperature of combustion, which can be accomplished by reducing intake charged air temperatures. This type of cooling, known as intake charge cooling, is in common usage in turbocharged diesel engines.
A common form that this type of system takes is two turbine-driven compressors combined with two intercoolers in series. The outside air passes through an inlet into the first compressor and from there into a first intercooler, which reduces the air temperature. This charged air then passes through a second compressor, powered by an exhaust driven second turbine, and into a second intercooler, which further reduces temperature. Next, the charged air passes through a first turbine, which reduces the temperature further when the charged air expands and also drives the first compressor. After this, the charged air flows through duct work leading to the intake manifold.
Another form of a system known in the art that cools the intake charge is one in which a closed-loop refrigeration system is used to cool the intake air. In this system, refrigerant fluid is circulated through a condenser to remove heat from the fluid and then compressed before entering evaporator coils. The evaporator coils are located at some point along the air intake stream upstream of the intake manifold and throttle valve to cool the air intake stream by heat exchange and thereby reduce the intake air temperature.
A significant problem with both these approaches is that, after the air is cooled but before it reaches the combustion chamber, the charged air will increase in temperature due to various heat sources. The intake air duct leading up to the intake manifold and the intake manifold itself are both in the high heat environment surrounding the engine compartment and are major contributors to this warming. This warmer air entering the combustion chamber, in turn, reduces the effectiveness of this strategy for reducing NO.sub.x emissions.